The present invention generally relates to a method for controlling data terminal equipment, such as a facsimile machine, and more particularly to a method for controlling data terminal equipment having a plurality of equalizer circuits. Further, the present invention is concerned with a data terminal equipment using such a method.
Recently, group-3 facsimile machines have been widely used. Group-3 facsimile machines have the specifications defined by the CCITT recommendations, and are connected to a public telephone line network. Group-3 facsimile machines are coupled to exchange systems provided in the public telephone line network via non-loaded cables. Thus, as the distance between the facsimile machine and the exchange system increases, high-frequency components of a signal carried via the non-loaded cable deteriorate. Particularly, when a received signal has a deteriorated frequency characteristic, it is impossible to demodulate a modulation signal used, in a high-speed modem (modulator/demodulator), for transmitting image information at a high bit rate. In this case, a data error will frequently occur, and the receiver cannot receive image information transmitted from a transmitter.
Conventionally, in a case as described above, the users of the group-3 facsimile machines call a service center and ask a serviceman to be dispatched. The serviceman measures the characteristics of the line between the facsimile machine and the corresponding exchange system and provides the facsimile machine with an equalizer for compensating for the line characteristics.
However, the above-mentioned maintenance procedure is very troublesome. Recently, the number of personal users of facsimile machines is increasing. Under the above environment, the above-mentioned maintenance procedure is not efficient.